The increase in number of diesel powered vehicles has led to greater concern for the
effects of their exhaust emissions. Engine manufacturers must now consider using
diesel particulate filters to make their engines meet the legislated limits. Diesel
particulate filters can remove more than 95% of the particulates from the exhaust
flow but require cleaning, known as regeneration.
This thesis describes the research and optimisation of the Autoselective regeneration
system for cordierite wall flow diesel particulate filters. The novel Autoselective
technology uses an atmospheric pressure glow discharge plasma to selectively
oxidise particulate matter (soot) trapped within the filter. The aim of this research was
to produce a regeneration system that can operate under all exhaust conditions with
a low energy demand and no precious metal dependence to compete with the
numerous pre-existing technologies.
The effect of discharge electrode type and position on regeneration performance has
been investigated in terms of regeneration uniformity, power requirement and
regeneration rate. The results showed that the electrode orientation had a large
effect on regeneration distribution and energy demand.
The electrode capacitance and breakdown voltage was shown to affect the choice of
power supply circuit because not all power supply topologies were suitable for
powering electrodes with >100 pF capacitance. A number of power supplies were
designed and tested, a voltage driven resonant transformer type supply was shown
to be optimal when used in conjunction with a swept frequency.
The current and frequency ranges of electrical discharges were continuously
variable, and their effect on discharge regeneration performance was studied. The
results showed that the discharge frequency had no effect on the regeneration
process but did affect spatial distribution. An optimised resonant transformer power
supply was designed that was ideally suited for the electrodes used. A novel power
modulation strategy, which used a switching frequency phase locked to the
~ iii ~
modulating frequency, was employed which extended the operating range of the
discharge to below 10 mA for electrode separations > 7.5 mm.
The heat flows within the filter and discharge during regeneration were analysed and
the filter damage process was linked to the heat released by the discharge inside the
filter wall. Other filter materials were compared based on the findings and Mullite
ceramic was identified as a potentially better filter material for Autoselective
The filtration efficiency is important and was observed to be affected by the
Autoselective process. The effect of the discharge on filtration efficiency was studied
and the mechanism of particulate re-entrainment was identified as a combination of
electrostatic and electro-acoustic forces.
The Autoselective technology was successfully implemented in both flow-rig and
on-engine tests. Results showed significant reduction in back-pressure for power
inputs of ~ 500 W. The understanding of the Autoselective regeneration system has
been improved and the research resulted in a novel method of filter regeneration.
A Doctoral Thesis. Submitted in partial fulfilment of the requirements for the award of Doctor of Philosophy of Loughborough University.